The present invention relates to a marker for identifying an object in a system which includes a light source and a detector of light reflected from the marker. More particularly, the present invention relates to an improved disk cartridge having a marker thereon providing for serial reflections of incident light by which the cartridge creates a reflection pattern at a detector distinguishing the cartridge from foreign objects.
Generally, removable disk cartridges for storing digital electronic information comprise an outer casing or shell that houses a rotatable recording medium, or disk, upon which electronic information can be stored. As used in this application the term disk cartridge refers to any data storage device including tape drives. The cartridge shell often comprises upper and lower halves that are joined together to house the disk. The disk is mounted on a hub that rotates freely within the cartridge. When the cartridge is inserted into a disk drive, a spindle motor in the drive engages with the disk hub in order to rotate the disk within the cartridge. The outer shell of the cartridge typically has some form of opening near its forward edge to provide the recording heads of the drive with access to the recording surfaces of the disk. A shutter or door mechanism is often provided to cover the opening when the cartridge is not in use to prevent dust or other contaminants from entering the cartridge and settling on the recording surface of the disk.
Disk drives for receiving removable disk cartridges, including conventional 3.5" floppy disk drives, must have some mechanism for detecting the insertion or presence of a disk cartridge in the drive. The actuator that carries the recording heads of the disk drive across the recording surfaces of the disk should not be allowed to move unless the presence of a disk cartridge is detected. In the prior art, mechanical switches are typically employed to detect the presence of a disk cartridge within the drive. Such switches are typically positioned such that when a disk cartridge is inserted filly into the drive, the cartridge contacts the switch, thereby providing an indication that the disk cartridge is present.
When a data storage cartridge is inserted into a drive it is important that the type of cartridge be recognized by the drive as the correct type of cartridge so as to insure safe and reliable use in the drive. Most removable cartridge drives (magnetic and optical) typically use approximately the same form factor cartridges, i.e., 3.5", 5.25", etc. Hence if one of these cartridges is inserted into the cartridge slot of the non-mating drive, there is a large probability that either the drive (heads, load mechanism. electronics, etc.) or the data on the disk could be damaged.
Also, some cartridges are "write protected" by the user to prevent accidental erasure of important data by writing over it. It is important to protect against operation of the drive when an incorrect or write protected cartridge is inserted.
Iomega Corporation, the assignee of the present invention, manufactures several models of data drives, including the Zip.TM. disk drive, which is available in a desk top and notebook computer version. These drives and the related data cartridges provide data densities 70 times greater than regular floppy disk drives. In order to provide the market place with this product, Iomega ingeniously designed a hard/Winchester drive technology that could read and write data on a removable flexible disk substrate. By providing a removable disk cartridge, Iomega was presented with the problem of foreign objects coming into contact with the extremely fragile read/write heads.
Generally, foreign objects include any object that is not intended for insertion into the data cartridge slot of a drive. For the Zip.TM. family of drives, foreign objects include any object that is not a Zip.TM. data cartridge. Such items include 3.5" floppies, candy bars, rulers, office index cards, sport collector cards, etc. Further, in the case of future versions of the Zip.TM. drives which might not be designed for use with cartridges for earlier versions of Zip.TM. drives, such cartridges for earlier drive versions could also be considered foreign objects.
"Foreign objects" which go undetected upon insertion into the drive may cause damage to or entirely destroy the delicately suspended read/write heads of the drive if it attempts to read/write data to the foreign object. If damaged, the heads can destroy subsequently inserted data cartridges and the data stored thereon.
Further, an undetected foreign object causes the motor in the drive to spin up. The motor has a hard pointed steel centering pin for mating and aligning valid data cartridges. The pin spins at approximately 3000 RPM and acts as a grinding wheel or drill on the surface of "foreign objects" which may be inserted. As a consequence, small particles of abrasive debris are generated in the drive. These particles may migrate into a later inserted valid data storage cartridge and destroy the data located thereon by scratching the soft magnetic storage media.
Recently, retroreflective materials have been developed. Typically, retroreflective material has many periodic miniature corner cubes, or spherical elements, which reflect light almost exactly upon its incident path. Retroreflective array materials are described in Jacobs, S. F., "Experiments with retrodirective arrays," Optical Engineering, Vol. 21, No. 2, March/April 1982; Rennilson, J., "Retroreflection--What is it and how is it used?" ASTM Standardization News, February 1982; and Venable, W. H., Stephenson, H. F. and Tersteiege, H., "Factor affecting the metrology of retroreflective materials," Applied Optics, Vol. 19, No. 8, Apr. 15, 1980, the contents of both of which are hereby incorporated by reference.
Applicant has recognized that a need exists for a cartridge marker that can be used to discern between valid cartridges and foreign objects. Further, there is a need for a data cartridge marker which can operate in multiple disk drive embodiments having varying emitter/detector arrangements. Also, there is a need for a marker which can be switched so as to allow for use in multiple drives.
It is therefore desirable to provide a data cartridge which provides for more reliable discerning of foreign objects. Further, it is desirable to provide a data cartridge which can adaptably be used in disk drives having varying emitter/detector configurations.